Found an oppossum walking in circles for hours? whats wrong with it?

My dad brought it in feeling bad for it bc its very cold out raining.. freezing at the same time. so anyways its in our bathroom in a big box right now.. we believe its dying? it hasnt moved much.. its droooling a lot.. we would have taken it to the vet but they are all closed around us seeings how its sunday. but anyways does anyone know what could be wrong with this thing? maybe it was poisoned? like i said when my parents first noticed it they jus saw it walkin in circles for over an hour.. until it jus stopped an jus sat in the drivway. .. just dont have the heart to stick it back out side an let it die.